06 October 2005

American Bullfrog (Rana catesbeiana)


I photographed this frog about a month ago next to a creek in College Park, Maryland. First I thought it was a Northern Green Frog (Rana clamitans melanota), but White & White1, indicates that the Green Frog has a pair of distinct dorsolateral ridges, which this specimen lacks. According to the same source, in the Bullfrog the dorsolateral ridges are lacking, but "a distinctive short fold of skin begins just behind the eye and curves down immediately behind the tympanum." A fold matching the description is clearly visible in the picture.

This website explains that "Like many species of Rana, the tympanic membrane is helpful in determining the gender of the individual. In females, the membrane will be roughly equal to the size of the eye and in males the membrane will be considerably larger." Based on the size of its tympanic membrane, this specimen is a female.

This species is native to the central and eastern United States and the southern portions of Ontario and Quebec. It has also been introduced into southern Europe, South America, and Asia.

More information on the American Bullfrog:
Animal Diversity Web

1. White & White. 2002. Amphibians and Reptiles of Delmarva. Tidewater Publishers.

1 comment:

Henry said...

Thats a nice pic. For comparison, Here is a green frog and a bullfrog I posted in April.